F# LazyList -> IList

Question

I'm creating a module that will be used by C# code, so I would rather not return the LazyList<> directly. If I did, the C# would have to reference the FSharp.PowerPack, which seems strange.

So I would rather return a IList<>, but when I try to do something like:

let x = LazyList.ofSeq {0..10}
let y = x :> IList<int32>

However, this gives me the error:

The type 'LazyList<int> is not compatible with the type 'IList<int>'

This leads me to believe that LazyList<> does NOT implement IList<>. Is this true?

What am I missing?

This [post](http://stackoverflow.com/q/9201402/2145211) could be helpful — Harrison, Oct 28 '13 at 15:30
`IList<_>` exposes things like `Count` which only make sense if the list is fully constructed, so it makes sense that `LazyList<_>` doesn't implement that interface. — kvb, Oct 28 '13 at 15:41
@kvb: I was taking DoctorJones (http://stackoverflow.com/questions/2689986/lazylistt-vs-system-lazylistt-in-asp-net-mvc-2/2690307#2690307) at his word a bit... But it definately makes sense that it wouldn't be able to do most of the functionality from `IList<>` — poy, Oct 28 '13 at 15:46
I think that's actually in reference to a different `LazyList<_>` class, not F#'s. — kvb, Oct 28 '13 at 16:04
There is `LazyList` in the ExtCore library, which also does *not* implement `IList` (https://github.com/jack-pappas/ExtCore/blob/master/ExtCore/Collections.LazyList.fs), but I think it would be a reasonable addition, so perhaps you could submit a pull request and use that? — Tomas Petricek, Oct 28 '13 at 16:30

score 4 · Accepted Answer · answered Oct 28 '13 at 15:37

4

It is true, LazyList does not implement the IList interface. It implements IEnumerable though.

[<Sealed>]
type LazyList<'T> =
   interface IEnumerable<'T>
   interface System.Collections.IEnumerable

answered Oct 28 '13 at 15:37

treze

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F# LazyList -> IList

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